/*
 * Copyright (c) 2003-2013, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.knopflerfish.util;

/**
 * The <code>Semaphore</code> class handles synchronization and waiting for
 * values.
 *
 * @author Johan Agat and Anders Rimen
 */
public class Semaphore {
  private Object value = null;

  private boolean closed = false;

  /**
   * Waits up to <code>timeout</code> milliseconds for this Semaphore to
   * receive a value.
   *
   * @return The value of the Semaphore or null if this Semaphore has been
   *         closed or if the specified timeout has expired.
   */
  public synchronized Object get(long timeout) {
    long start = Timer.timeMillis();
    while (!closed && value == null) {
      try {
        long t = Timer.timeMillis() - start;
        if (t < timeout)
          wait(timeout - t);
        else
          return null;
      } catch (InterruptedException ignore) {
      }
    }
    return value;
  }

  /**
   * Sets the value of this Semaphore. This will cause all blocked
   * calls to {@link #get(long)} to return the value. If {@link
   * #set(Object)} is called several times with a short or no delay
   * between the calls, the exact value returned by a given blocked
   * call to {@link #get(long)} is not deterministic.
   *
   * @param v The new value.
   */
  public synchronized void set(Object v) {
    if (closed)
      return;
    value = v;
    // setCount++;
    notifyAll();
  }

  public synchronized void reset() {
    value = null;
  }

  public synchronized void close() {
    value = null;
    closed = true;
    notifyAll();
  }

}
